1. Field of the Invention
The present invention relates to a flat-plate patch antenna including a ground plate, a radiating element and a wave guide element.
2. Prior Art
Despite having a simple structure, circular patch antennas are known to have superior directional and high gain characteristics. Specifically, a circular patch antenna can be constructed merely by installing a circular wave guide element in front of a circular radiating element via an insulator or dielectric.
In conventional circular patch antennas, the ground plate, radiating element and wave guide element are constructed as a single unit, so that directionality (or directivity) is superior in the direction of a straight line drawn between the center of the radiating element and the center of the wave guide element.
FIG. 6 is a schematic view of a conventional circular patch antenna.
This antenna includes a ground plate 10a, a radiating element 20a, and a wave guide element 30a. In the Figure, the line La drawn between the center 21a of the radiating element 20a and the center 31a of the wave guide element 30a is parallel to the line drawn perpendicular to the ground plate 10a. As a result, the directionality is stable with respect to the ground plate 10a; and if the ground plate 10a is attached to a vertical wall, the directionality of the antenna is fixed in a horizontal direction.
However, this type of antenna has some drawbacks. When the antenna is attached to the wall of a building, it may be impossible to match the directionality of the antenna with the direction of a desired beam. When the ground plate of the antenna is fixed so that it faces a prescribed direction, it may also be impossible to match the directionality of the antenna to the direction of a desired beam. This problem occurs not only in circular patch antennas, but also in flat-plate antennas having other shapes.